This information was first posted in our "Question of the Week" area.
What’s MOST important to Koi during a power outage? Quick answer – AIR! Koi require oxygen to live, and without an air pump or a water fall running, they will quickly consume all available oxygen in the pond and die!
Water with an oxygen concentration of less than 3 mg/l will generally not support fish. When concentrations fall to about 3-4 mg/L, fish start gasping for air at the surface or huddle around the water fall (higher concentration points). Bio‑converter bacteria may start to die, dumping toxins into the water and compounding the lack of oxygen to the fish. Levels between 3 and 5 mg/l can normally be tolerated for short periods. Young Koi generally have less tolerance to poor water conditions including low oxygen, although larger Koi consume considerably more oxygen, and are generally the first to die in a power outage. Above 5 mg/l, almost all aquatic organisms can survive indefinitely, provided other environmental parameters are within allowable limits. Ideally, our ponds should be at or near oxygen saturation at all times.
Remember that near freezing water holds about twice as much oxygen as hot water near 90°. So the time you have to get oxygen to the pond is longer when the water is cold. Generally, the most important thing to do during a power outage is to get an air pump running in the pond, and you have longer to accomplish this if the water is cold. The beneficial bacteria in the filter will also be affected by the lack of oxygen during a power outage. It is critical to carefully test the pond for ammonia for the next few days after power is resumed, and use an ammonia binder such as Chlor-Am-X©, or water changes, as needed, until the filter recovers. The pond should subsequently also be tested for Nitrite if ammonia is detected. It is helpful to stop feeding whenever ammonia or nitrite are present in the pond until the filter if fully recovered.
Even a bait bucket aerator running on D-cell batteries can provide enough oxygen to keep Koi alive for a while, but obviously owning a generator and standard Koi pond air pump should be standard safety precautions for any Koi owner where power outages may occur.
So why do wild ponds have healthy fish populations when there is no waterfall or air pump to supply oxygen? The answer has to do with stocking density. In a normal wild environment, there is an average of only 1 fish per million gallons, and there is a much larger air/water interface area (the surface of the pond). Oxygen transfers from the air only at the surface of the pond, and is enhanced by wind stirring up the water. Oxygen may also be produced by certain pond plants, but normally plants produce oxygen as a byproduct of photosynthesis during the day, and then consume oxygen at night. Large blooms of algae or other plants often upset the pond balance and actually consume more oxygen then they produce, resulting in fish die-offs.
To learn more about oxygen in ponds and how all water quality parameters interact, please consider taking the K.O.I. course #201 – Water Quality. You may purchase this course as reading material only, or you may find that interacting with the instructor and doing homework and tests enhance your understanding of the subject.